The present invention relates to a connection between two shaft ends situated coaxially one behind the other of a gas exchange valve of an internal combustion engine and of a valve actuator, where at least one coupling member at least partially surrounds the shaft ends.
A connection is known from published patent document EP 0 279 265 B1, where the coupling member includes two half-shells whose radially external peripheral surfaces are cylindrical, and whose radially internal peripheral surfaces are conical in a manner complimentary to the piston rod ends of the valve actuator, which are tapered conically with respect to one another, and to a shaft of the gas exchange valve. To prevent the two half-shells from falling apart, a cylindrical coupling sleeve is held to the half-shells by the axial prestress force of a valve spring which is supported on the bottom of the screw sleeve and is pushed over them, and the shaft of the gas exchange valve extends through an opening in the bottom of the screw sleeve. The two shaft ends, which are tapered relative to each other, have at the extremity flanges that are widened in a plate-like manner and grip the coupling member formed by the half-shells from behind, so that the two shaft ends are connected to one another by the coupling member in a form-locking manner. At the form-locking junction between the conical runout of the shaft ends and the extreme flanges, the cross-section is weakened in each case by a distinct groove, which has a negative effect on the fatigue strength of the connection. This represents a significant disadvantage especially with regard to the high number of load changes that gas exchange valves of internal combustion engines are subjected to.
Due to the frictionally engaged connection between the coupling member and the shaft ends, no undercuts are necessary such as groove-like indentations which weaken the cross-section of the shaft ends and/or of the coupling member. Consequently, the connection of the present invention is distinguished by a high degree of fatigue strength.
According to an exemplary embodiment, the prestress applied to the coupling member by the compressing member may be adjustable. For this purpose, the compressing member includes at least two conical compressing sleeves which may be axially screwed against one another and have conical surfaces that may be wedged against conical compressing surfaces formed on the radially external peripheral surface of the coupling member. A defined radial prestress may be generated between the coupling member and the shaft ends as a function of the degree of tightening of the conical compressing sleeves. This may be advantageous with regard to the surface conditions that may differ depending on the gas exchange valve or the valve actuator and to the correspondingly different friction coefficient in that the radial prestress necessary for slip-free static friction locking may be adjusted.
Viewed in the circumferential direction, the coupling member has a multi-part design and preferably includes at least two half pipe-shaped coupling wedges, which complement one another to form a sleeve. Each coupling wedge has on its outer peripheral surface two compressing surfaces situated radially one behind the another and expanding conically with respect to one another, and each compressing surface may be assigned to one conical surface of one of the conical compressing sleeves. Both conical compressing sleeves may be expediently provided with a contact surface for a screw tool.
According to a further embodiment, positioning projections and positioning recesses that preferably intermesh with play may be provided on the coupling member and on each shaft end for positioning the coupling member on the shaft ends. This ensures that the coupling member may be compressed in a defined position with respect to the shaft ends, and may result in a balanced surface covering. On the other hand, the loose intermeshing of the positioning projections and recesses, reduces fatigue strength-lowering notch stresses. According to an exemplary embodiment, the radially internal, cylindrical peripheral surface of the coupling wedges has annular protuberances that extend in the circumferential direction, and each annular protuberance may be assigned to an annular groove of a shaft end. The annular protuberances and annular grooves have an essentially semicircular cross section, the inner radius of the annular grooves being greater than the outer radius of the annular protuberance in order to prevent direct material contact as much as possible, and to keep the notch stresses caused by the annular grooves as low as possible.
Finally, the connection between the valve actuator and the gas exchange valve may be situated in an accessible region outside of a valve actuator housing. Therefore, in the event that repairs may be needed, it may be very easy to replace a gas exchange valve or a valve actuator, and it may not be necessary to dismantle the valve actuator.